At present, the LED preparation technology used widely is to package an LED chip in blue light or ultraviolet light and the like with a fluorescent powder layer and an epoxy resin housing, and by adjusting the type of the chips, as well as the components and the proportion of fluorescent powders, red, orange, yellow, green, blue and other multi-color light and white light can be emitted.
In terms of the prior art, the composition and the structure of an LED have some key problems which need to be solved urgently.
Currently, the vast majority of LED packaging materials is epoxy resin or organic silicon. The application form of the fluorescent powder in the LED is mainly as follows: the fluorescent powder and the epoxy resin or the organic silicon as a matrix are stirred and mixed under liquid state, and then the mixture is coated on the surface of the LED chip. The housing made of epoxy resin or organic silicon material is finally applied for packaging.
There are some problems in the above-mentioned application method of the fluorescent powder and the packaging material:    (1) As the fluorescent powder and silica gel are physically mixed under liquid state, the fluorescent powder will settle inevitably; furthermore, the larger the particle size of the fluorescent powder is, the more obvious the settlement becomes.    (2) With the rise in the temperature of an element during the using process, yellowing is easy to occur because the softening point of the epoxy resin is very low (55-95) and the heat conductivity thereof is poor, as a result, the transparency is affected and the performances and the service life of the LED are further reduced.    (3) As the fluorescent powder is directly settled on the surface of the LED chip, back scattering of light can be generated during the light-emitting process, light loss (20%-30%) is further caused, the stability in the performances of the LED is affected and the service life of the LED is further shortened.    (4) The refractive index of each of the epoxy resin material and the organic silicon material is less than 1.5 generally, which is greatly different from the refractive index of the LED chip (the refractive index is 2-4), thus total reflection is liable to occur and the brightness of the LED is further seriously affected; furthermore, the price of the organic silicon is high.
In order to solve the above-mentioned technical problems, one way is to mix the fluorescent powder with the epoxy resin or the organic silicon, and 0.1-10% of inorganic matter fine powder (such as silicon dioxide powder) which can not react with the mixture is additionally added. By adopting the method, white light LED with uniform light color can be obtained, but the problems of rise in the temperature due to continuous lighting of the blue light LED, deterioration of wavelength conversion material and insufficient light efficiency are still present.
As the transparent ceramic material of the invention, such as magnesium aluminate spinel (MA), yttrium aluminum garnet (YAG), yttrium oxide, aluminum oxynitride and the like, has a cubic structure, the transparent ceramic material can be made into transparent ceramic; furthermore, the transparent ceramic material has the characteristics of good corrosion resistance, insulativity, high heat conductivity, high melting point, high hardness and high strength, and the excellent performances of the transparent ceramic material enable a device manufactured by the transparent ceramic material to be strong in environmental suitability, wear-resistant and impact-resistant. After a long-term use, the transparent ceramic material has few surface damages and can still keep high transmission, thereby being the ideal packaging optical material. However, although aluminum oxide and other materials can also be used for manufacturing the transparent ceramic, the hexagonal crystal structure decides that the current technology can only realize semi-transparence and such materials are very difficult to be used here.
Chinese patent CN100565000C discloses a method for manufacturing a white light LED with YAG transparent ceramic. But the patent does not utilize the transparent ceramic which is formed by firing for packaging the LED and only applies a rare earth-doped YAG ceramic powder to coat the LED chip so as to avoid yellow light ring, blue light ring and other problems. The method is only different from the traditional method in that rare earth-doped YAG transparent ceramic particles are used for replacing the fluorescent powder, and the heat dissipation, the light-emitting uniformity and the like of the LED are not improved.
Chinese patent CN100389504C discloses a YAG wafer type white light LED and packaging method thereof. A YAG single wafer is utilized for converting part of blue light which is emitted by a GaN-based inorganic semiconductor LED chip to the light in another wave band or various wave bands, and then the remaining unconverted blue light emitted by the LED chip is mixed with the light in the ideal wave band after the conversion through the single wafer for generating white light. The technical problem that it is very difficult in the traditional white light LED device technology to control the dispersivity of phosphor powder in silicon grease type or resin type sealants so as to finally lead to non-uniform white light of the LED device can be solved by the uniformity of the single wafer to obtain single and high-quality white light. However, as the YAG single wafer is longer in growth cycle and high in cost and the doping of rare earth element is difficult to control, the patent is more difficult to be applied in production.